Oxide semiconductor-metal contact resistance elements

ABSTRACT

New oxide semiconductor-metal contact resistance elements having remarkably stable volt-ampere characteristics are provided. The contact resistance elements comprise oxide semiconductors which have negative resistance and also possess such thermister constant B*K and specific resistance RoK Omega at 273*K as satisfy the relation B X Ro &lt; OR = 104K Omega .*K, and metals which are highly anticorrosive and have high electric conductivity, attached thereto, and are based on utilization of the property of the contact surfaces between the oxide semiconductors and the metals.

United States Patent Tachibana et al.

[75] Inventors: Kan-lchi Tachibana; Michihiro Nishioka; Mikiya Ono, allof Kitakyusku,..lapan [73] Assignee: Mitsubishi Mining & Cement Company,Ltd., Tokyo, Japan [22] Filed: May 21, 1973 [21] Appl. No.: 362,461

[30] Foreign Application Priority Data June 22, 1972 Japan 47-62588 [52]US. Cl. 338/20 [51] Int. Cl. H0lc 7/10 [58] Field of Search .1 338/13,20, 22, 25;

252/512-513, 518-520; 317/234 N, 238, 235 K, 235 Q; 357/28, 57

[56] References Cited UNITED STATES PATENTS 2,027,277 1/1936 Habann338/20 "I'M-"I'll Sept. 16, 1975 2,590,894 4/1952 Sanbom 338/203,105,800 10/1963 Watanabe 338/22 SD 3,310,766 3/1967 Downong et a].338/20 3,393,448 7/1968 Harget et a1. 338/22 R 3,511,786 5/1970 Brixner338/25 X Primary Examiner-C. L. Albritton Attorney, Agent, orFirm-Edward J. Brenner 1 Claim, 4 Drawing Figures OXIDESEMICONDUCTOR-METAL CONTACT RESISTANCE ELEMENTS BACKGROUND 01-" THEINVENTION This invention relates to oxide semiconductor-metalcontact'resistance elements comprising oxide semiconductors and metalsor alloys attached thereto. The contact resistance elements of thisinvention have the same remarkably stable volt-ampere characteristics asthose of non-linear resistors,- and these volt-ampere characteristicsare based on the property of the contact surfaces between the oxidesintered bodies and the metals or alloys, consequently the contactresistance elements can be made to be small-sized.

Conventional non-linear resistors (the term non linear resistor ishereinafter referred to as varistor) comprise silicon carbide varistors,silicon varistors, barium titanate varistors and the like.

In general, the volt-ampere characteristic of such a varistor is givenby the following equation (I):

where I is the current flowing through the varistor, V is the voltageacross the varistor, V is the voltage applied to the opposite surfacesof the varistor at l=l mA, that is, a threshold voltage, and. a, anindex representing non-linearity is usually 3-5.

Silicon carbide varistors become worse in characteristics with smallerin size, then. exhibiting a values less than 3. Silicon varistors andbarium titanate varistors are bothv able to be small-sized, but arelimited in uses because V values thereof are as low as O.5-l.2V.

This invention has been devised to overcome the defects of i theconventional non-linear resistors as I described hereinabove.

SUMMARY OF THE INVENTION A primary object of this invention is toprovide a nonlinear resistor which has a remarkably stable voltamperecharacteristic.

Another object of this invention is to provide a nonlinear resistorwhich is able to be small-sized.

A further object of this invention is to provide a nonlinear resistorwhich is inexpensive in cost.

According to this invention, there is provided an oxidesemiconductor-metal contact resistance element comprising an oxidesemiconductor, said oxide semiconductor having negative resistance andalso possessing the thermister constant BK and the specific resistancevalue R Kfl at 273K that satisfy the relation BXR l0,000KQ-K, and ametal, said metal being highly anti-corrosive and having high electricconductivity, attached thereto.

In general, the relation between the resistance R KQ at 7K, R KO and BKof an oxide semiconductor is given by the following equation (2):

l l R= R exp B :l

The equation (2) is not always applicable to any temperature range, butthis invention relates to R and B in the temperature range which theequation 2) is applicable to.

The contact resistance element of this invention is characterized inthat it has an excellent characteristic which does not be lowered whenmade to be smallersized. Namely, the contact resistance element of thisinvention has a remarkably stable characteristic because V value thereofis lO-2OV at I =5mA and also a is about 5, and can be easily made to besmaller-sized.

The invention is now explained in detail with reference to the attacheddrawings.

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS FIG. 1 is a plan view of apreferred embodiment of this invention.

FIG. 2 shows a section view thereof.

FIG. 3 shows a volbampere characteristic suitable for a non-linearresistor.

FIG. 4 shows a volt-ampere characteristic unsuitable for a non-linearresistor.

In FIG. 3 and FIG. 4, voltage E is plotted as abscissa and current I asordinate.

DETAILED DESCRIPTION OF THE INVENTION The oxide semiconductors as onecomponent of the contact resistance element of this invention which havenegative resistance and also possess such a specific resistance R KQ at273K and a thermister constant BK that satisfy the relation BXR IOKQ'Kare preferably sintered bodies of the mixtures such as iron oxide andcopper oxide, cobalt oxide and nickel oxide. iron oxide and titaniumoxide and the rest, and the metals or alloys as another componentthereof which are highly anti-corrosive and have high electricconductivity are preferably such metals as copper, Zinc, nickel etc., orsuch alloys as brass. phosphor bronze, German silver etc. Therefore, thecomponents of the contact resistance element of this invention are bothinexpensive in cost. n I

Now, the contact resistance element of this invention is explained withreference to the attached drawings.

FIG. 1 shows a plan view of a preferred embodiment of this invention.FIG. 2 is a section view thereof.

The invention provides a contact resistance element. as shown in FIG.l-and FIG. 2, manufactured easily by making small holes in the oxidesintered body I, attaching the metal or alloy pieces 2, 2 to the oxidesintered body 1 through the small holes and fixing the whole with asuitable insulating coating material 3 such as epoxy resin. The contactresistance element of this invention has such a remarkably stablevolt-ampere characteristic as shown in FIG. 3, proving to be suitablefor a non-linear resistor.

This invention, as described hereinabove. provides a contact resistanceelement which is inexpensive in both raw material cost and manufacturingcost and can be made to be small-sized without lowering the remarkablystable characteristic thereof, consequently it is industrially of greatvalue.

The invention will be understood more readily with reference to thefollowing example. However, the example is intended to illustrate theinvention and is not to be construed to limit the scope of theinvention.

EXAMPLE 7 The sintered body is prepared by a conventional technique. Thestarting material in the composition defined in Table l is respectivelymixed in a pot mill so as to produce a homogeneous mixture. The mixtureis dried in a dryer, pressed ina mold at a pressure of about 1,000kg/cminto a disc of 10mm in diameter and lmm in thickness. The molded disc issintered in air at above l,0OC, thus the sintered disc 1 is obtained.

A contact resistance element is manufactured, as shown in FIG. 1, bymaking two small holes of about lmm in diameter in the sintered disc 1,attaching the copper pieces 2, 2 to the sintered disc 1 through the twosmall holes respectively and fixing the whole with epoxy resin 3.

As the thus manufactured contact resistance element has a surfacebarrier existing at the contacting surface between the sintered disc 1and the copper piece 2 as described hereinabove, the resistance Rthereof is high at the low voltage and the current varies as the voltageincreases as shown in FIG. 3. The measured values of R, R and a of thecontact resistance element are shown in Table 1. Further, the values ofthe resistance R KO. and thermister constant BK of the sintered body Imeasured in a conventional manner are also shown in Table I, togetherwith those of R XB.

As Table 1 shows, the values of R B of the sintered bodies l-lV are allnot more than l0,00()KO-K. The contact resistance elements manufactured,as shown in FIG. I, by using these sintered bodies show all theremarkably stable volt-ampere characteristics as shown in FIG. 3, thusproving to be suitable for a non-linear resistor.

For comparison, the sintered bodies are prepared in the same manner asthe above mentioned example from the starting materials in thecomposition defined in Table 3. The measured values of R B and R arealso shown in Table 2.

As Table 2 shows, the values of R XB of the sintered bodies V-Vlll areall larger than 10,000Q-K. The contact resistance elements manufacturedby attaching the copper pieces to the sintered bodies in the same manneras the above mentioned example show all the unstable volt-amperecharacteristics as shown in FIG. 4, thus proving to be unsuitable for anon-linear resistor.

What is claimed is:

1. An oxide semiconductor-metal contact resistance element comprising adisk-like oxide semiconductor having a surface barrier resistance, saidoxide semiconductor having negative resistance and also possessing aspecific resistance value R KQ at 273K and a thermister constant BK thatsatisfy the relation R XB l0,000KQ-K, and two pieces of metal brought indirect and fixed contact therewith respectively, said metal being highlyanticorrosive and having high electric conductivity.

1. AN OXIDE SEMICONDUCTOR-METAL CONTACT RESISTANCE ELEMENT COMPEISING ADISK-LIKE OXIDE SEMICONDUCTOR HAVING A SURFACE BARRIER RESISTANCE, SAIDOXIDE SEMICONDUCTOR HAVING NEGATIVE RESISTANCE AND ALSO POSSESSING ASPECIFIC RESISTANCE VALUE R0K$ AT 273*K AND A THERMISTER CONTANT B*KTHAT SATISFY THE RELATION R0XB $ 10,000K$*K, AND TWO PIECES OF METALBROUGHT IN DIRECT AND FIXED CONTACT THEREWITH RESPECTIVELY, SAID METALBEING HIGHLY ANTICORROSIVE AND HAVING HIGH ELECTRIC CONDUCTIVITY.